| Multifunctional cement-based materials for combined structural and electrical applications have been developed for use in smart structures. The electrical functions include sensing (strain, damage and temperature sensing) and electromagnetic interference shielding. They are based on phenomena such as piezoresistivity, thermoelectricity, piezoelectricity, pyroelectricity, and radio wave reflection.; The cement-based materials attain the non-structural functions by the use of electrically conductive additives, which include discontinuous fibers (carbon and steel), continuous fibers (carbon) and graphite particles. The materials can be in monolithic, coating and junction forms. The junction form provides cement-based pn-junction, which serves as a thermocouple and exhibits current rectification characteristic.; By using appropriate conductive admixtures, absolute thermoelectric power ranging from -68 to +26 muV/°C, shielding effectiveness up to 70 dB (1.5 GHz), piezoelectric coupling coefficient up to 3 x 10 -11 m/V (10 kHz) and pyroelectric coefficient up to 6 x 10-8 C/m2.K (10 kHz) have been attained. Steel fiber of diameter 60 mum is particularly effective for enhancing the thermoelectricity. Steel fiber of diameter 8 mum is particularly effective for providing shielding, piezoelectricity and pyroelectricity. Carbon fiber of diameter 15 mum is particularly effective for enhancing piezoresistivity.; Piezoresistivity in carbon fiber cement is similar whether the resistance is measured in the longitudinal or transverse direction. Resistivity increases upon tension and decreases upon compression. Piezoresistivity allows observation of defect dynamics (defect generation, healing and aggravation) during repeated loading, whether the cement contains fiber or not.; Thermoelectricity provides information on the electrical conduction mechanism. Carbon fiber in cement provides hole conduction. Steel fiber of diameter 60 mum in cement involves carrier scattering, such that its effect depends on the fiber volume fraction. |
